1. Field of the Invention
The present invention relates to a modulation/demodulation method based on a Run Length Limited (RLL) method capable of converting data bit streams to be recorded on an optical recording medium, etc. into bit streams whose format is adequate for recording marks, and relates to a modulation/demodulation apparatus using the same.
2. Description of the Related Art
As a recording medium for recording various format data, a tape which is a magnetic medium, an optical recording medium, etc. are known. A compact disk (CD) among the recording medium is widely used. In addition, as the standard specification of a digital versatile disk (DVD) is developed, the use of the optical recording medium is being increased. As the optical recording medium, various kinds of the optical recording medium such as a CD-ROM, DVD-ROM, which are read-only type, a CD-R, DVD-R, which are writable-once type, a CD-RW, DVD-RAM which are re-writable type, and an optical magnetic type disk, etc. are disclosed until now.
When recording digital data on the above-mentioned optical recording medium, the data are to be modulated for decreasing a drop-out effect of a signal, obtaining a reproduction reliability of a recording signal, and removing a DC component of the signal. An RLL modulation method is generally used when recording digital data to modulate data to be recorded. In the RLL modulation method, the Eight-to-Fourteen Modulation (EFM) method, suggested by Philips, is most widely used.
The EFM method is directed to a modulation method for converting a 8-bit data into a 14-bit code. The modulated code has 2 to 10 zeros between adjacent 1s of the code. This condition may be expressed in a general form like RLL(2,10).
Since the EFM code requires additional three bits for controlling a Digital Sum Value (DSV), an encoding ratio decreases to {fraction (8/17)}, it is not proper for increasing the recording density of a recording medium. In addition, the EFM method is too sensitive to jitters during the demodulation of data, so that the EFM method is not adequate for the data modulation method for a high-density recording medium.
A New Efficient Modulation (NEM) method has been proposed by Toshiba Union to apply to the high-density optical disk. The NEM method modulates a 8-bit data to a 15-bit code and has a limitation of RLL(2,12). Various modulation methods have been researched except for the NEM method.
In addition, there are still much differences in the reproducing error rate in the modulation methods having a good result for enhancing recording density of a disk medium. Therefore, it is urgently demanded to develop a new modulation method providing high-density of a recording medium and reducing reproduction error rate.
It is an object of the present invention to provide a modulation/demodulation method of a digital data, and apparatus using the same which are capable of enhancing a recording density of a recording medium and implementing an accurate reproducing operation which is rarely affected by a jitter factor.
To achieve the above objective, there is provided an RLL data modulation method to form more than two bit-groups for a modulation data and to associate a bit-group with one of two recording phases in such a manner that the length of the bit-group recorded into one of the recording phase is quantized by two or greater integer step.
To achieve the above objective, there is provided a demodulation method which is directed to removing a trigger deviation due to jitters by accomplishing such a phase-compensation operation as replacing a bit group whose bit length does not belong to a quantized value with a quantized-length bit group.
Additional advantages, objective and features of the invention will become more apparent from the description which follows.